Rectifier and the like



Feb. 11, I936. E. F. RANDALL 2,030,396

RECTIFIER AND THE LIKE v Filed Dec. 30, 1925 2 Sheets-Shea? l Feb. 11, 1936'. E. F. RANDALL RECTIFIER AND THE LIKE Filed Dec. 30 1925 2 She etsSheet 2 Patented Feb. 11, 1936 UNITED STATES PATENT OFFICE RECTIFIER AND THE LIKE Application December 30, 1925, Serial No. 78,427 Renewed July 22, 1933 15 Claims.

This invention relates to the rectification of alternating electric current or to amplification or modulation of current and seeks to provide a construction wherein such action will take place efliciently and continuously over long periods of time without requiring an incandescent cathode and the heating mechanism therefor. This is accomplished by using as a cathode a material having electro-positive characteristics and also capable of producing a conductive vapor. It is well known that the electro-positive alkaline earth metals and the alkali metals will part with electrons much more freely than will electronegative conductors.

According to this invention, therefore, use is made of such electro-positive electron emitting substances combining therewith a vapor forming metal which becomes, when the device is in operation, the main current carrying conductor between the anode and cathode terminals. A vapor forming metal which has been found satisfactory in practice is mercury and various electro-positive materials may be used, such as calcium, barium, strontium or other alkaline earth metals or alkali metals or mixtures of these materials. Where a glass tube is used as a container, sodium is not suitable because of its capacity of attacking the glass under certain conditions.

These various electro-positive materials form alloys or amalgams with the mercury and also act to lower its vapor tension. An electro-positive material which is particularly well suited for the purpose is barium and further description of this invention will be more particularly directed to a rectifier employing this material, though it should be understood that the invention is not limited to rectifiers or to this particular material.

For a more complete understanding of this invention, reference may be had to the accompanying drawings in which Figure 1 is an elevation partly broken away of one form of rectifier embodying this invention.

Figure 2 is a perspective partly broken away of one member which is utilized to form one portion of the tube or container.

Figure 3 is an elevation of another member of the container.

Figure 4 is a section on line l4 of Figure 1.

Figure 5 is a sectional detail similar to a portion of Figure 1, but on a larger scale.

Figure 6 is a VlCW similar to Figure 1, but showing a modified construction.

Figures 7 and 8 are perspectives of certain poptions of a different form of device utilizing both sides of the current wave.

Figure 9 is a section on line 99 of Figure 7. Figure 10 is a section similar to Figure 9, but showing a construction for three phase current. 5 Figures 11 and 12 are wiring diagrams of the connections for the constructions of Figures 1 to 6 and 10.

Figure 13 is a view similar to Figure 1, but showing another construction for utilizing both 10 sides of the current wave.

Figure 14 is a section on line "-44 of Figure 13.

Figure 15 is a wiring diagram for the construction shown in Figures 6 to 9 and in Figures 13 15 and 14.

Figure 16 is a cooling curve for a barium alley or inte-rmetallic compound.

The mercury barium alloy or amalgam is in the form of a normally solid metallic compound 20 and may be prepared in the following manner.

A sodium amalgam is first prepared by placing small pieces of sodium in a dish with mercury and stirring it when suddenly there is a flash as the sodium combines with the mercury in an exothermic reaction. There may be metallic compounds as well as an amalgam formed between the two metals. This sodium mercury combination is then placed in a saturated solution of barium chloride in water, (or where strontium is employed a solution of strontium chloride) when it immediately begins to decompose, the sodium being displaced by the alkaline earth and probably going intosolution as sodium chloride or sodium hydroxide. After considerable action in the solution the amalgam changes its appearance and becomes quiescent. It should then be washed and dried in absorbent paper and then heated to still further dry it and cause impurities to float to the surface. These may be skimmed off and the alloy formed into an ingot which when cool is solid. Any sodium (or potassium) left in the amalgam seems not to hurt the alloy, but tends to help out by its purifying action on the rare gas used in the tube or container, as will later appear, and also appears to help in producing electrons easily for the rectifying or other action of the device.

Another method of making the amalgam is to use a pool of mercury as a cathode with barium or strontium chloride in saturated solution with water as an electrolyte. The mercury cathode is connected to a battery through a platinum wire sealed in a glass tube which is placed in the electrolyte with the wire in contact with the mercury in the bottom of a jar in which the chloride electrolyte is placed. From one to two amperes of current are then passed through the solution so as to deposit the alkaline earth metal into the mercury. Strong fumes of chlorine gas escape during this process. This action goes along smoothly for a little time when suddenly the solution begins to boil and after the decomposition has proceeded for perhaps an hour there can be seen floating on the surface of the pool, silvery cubes of alkaline earth mercury compound, they being lighter than the rest of the amalgam. These crystals are skimmed off from the surface when enough, have accumulated and are separated from as much of the liquid as pos sible and dried in absorbent paper and then refined by heating and casting into an ingot.

There appears to be a chemical action between the mercury and the alkaline earth metal forming an inter-metallic compound with a portion of the amalgam, this chemical compound in the case of barium being probably represented by either BaHgiz or BaHgm or both. This solid alloy or compound, if melted under vacuum conditions and sealed to prevent oxidization and heated until quite fluid and then permitted to cool slowly, has a cooling curve as shown in Figure 16, the abscissas representing time in minutes and the ordinates degrees centigrade. The temperature curve being plotted, it is found that a break occurs in the curve at 130 C., and at about 109 there is a sudden rise to 114 and then a gradual fall to room temperature. This portion from 109 to 114 appears to be the supercooling portion of the curve at which solidification of the material takes place. The temperature range between 109 and 130 probably represents that which is concerned primarily in the present invention.

Referring now to Figures 1 to 5, indicates a glass tube or container having a reentrant upper portion il. This, as shown in Figure 2, may be formed as a tubular glass member, the main portion [2 of which is of smaller diameter than the outside of the container. At the upper end of this portion I2 is an outwardly directed flange portion 13 which may be fused to the upper edge portion of the outer wall of the tube ill in such a manner that the portion l2 extends inwardly thereof. This member H is provided with a central hollow stem I through which air may be exhausted from the interior of the container between the portions II and I0 and a gaseous medium such as helium or neon let in under reduced pressure. This tubular portion M as shown leads to the interior of the tube l0 through an opening I5 and through the lower wall of this portion I I a conductor I6 is sealed, this conductor leading to an anode such as carbon or a piece of refractory metal wire such as tungsten. The portion II also has a depending fin or rib 2| to which is attached a block of insulation shown detached in Figure 3 as at 25.

Referring to Figure 3, it will be seen that this insulation, which may, if desired, be made of lavite or other similar refractory material. is provided with a series of annular surface portions 26, 21, 28, 29 and 30 of progressively decreasing circumferences, each one of these annular portions being preferably provided with an annular groove such as 3|. Surrounding the portions 26, 21, 28, 29 and 39 are the upper ends of concentric metallic tubes 32, 33, 34, and 36, all these tubes being concentrically arranged with reference to the anode 20. These tubes may be fixed to the member 25 by indenting portions thereof whichlap past the surface portion of the block 25 into the grooves 3| either continuously around their circumferences or at intervals as by the use of a prick punch as shown in Figure 5 at 31', or they may be cemented in position as by the use of a mixture of sodium silicate and barium sulphate or other suitable cement.

The outer tube 32 or cathode terminal is considerably longer than any of the others and dips into a pool of the mercury barium amalgam which is shown at and which lies in the bottom of the tube I0, the device being maintained in upright position during operation. To this outer tubular member 32 is fixed the negative conductor 4!, this being suitably sealed in the wall of the tube as at 42. These tubular members 32 to 36 should be of conducting material such as metal or carbon and may Well be thin iron. It will be noted that they are graduated in circumference, this being done partly to give a uniform potential gradient along the insulating material separating the tubular members from each other and the central anode and that they extend away from and below the block 25. All solid metal parts should be heated in vacuo or in a reducing atmosphere to eliminate dissolved or occluded gases therefrom. Preferably they are heated to bright red in a vacuum furnace before the parts are assembled and heated again after the parts are assembled and evacuated on the pump before the amalgam is put in, and then again but to a less extent after the amalgam has been introduced.

Within the outer tubular member 32 there remains a space for an electrical gaseous discharge between the anode and the amalgam cathode surface, the outer tubular member and the amalgam surface forming the cathode terminal cup. It may also be desirable to provide a vent opening, as 38, through the upper portion of the tube 32 to relieve any pressure which might otherwise blow the amalgam out from its lower end. The metallic compound in the cathode besides forming one electrode also supplies a. metallic vapor which serves as the main conducting material between the anode .and the cathode, but in order to start the tube functioning, it is necessary to heat the metallic mixture to form a certain amount of metallic vapor. In order to accomplish this a monatomic gas such as helium, neon, or argon, or an organic gas such as carbon monoxide may be admitted to the interior of the tube at suitable low pressure be fore it is sealed off from the evacuating pump. This gas allows an electric gaseous discharge to take place between the anode and cathode when a suitable voltage is applied to the two terminals of the device. This combination of gas and electrodes will permit an alternating current to fiow during one half cycle but will suppress the other half cycle, thus resulting in an intermittent direct current. This gaseous discharge causes the mixture of metals which is normally solid to melt and a vapor is given oil which increases its pressure with increase of temperature until the metallic vapor pressure is sufliciently high to be the main current conducting material, and as soon as this occurs the resistance of the rectifier greatly reduces so that there is an increase in current and .also a decrease in the losses and heating of the tube. Thus it may take in the neighborhood of 200 volts across the tube terminals to start the gas ionization, while 10 volts may be sufficient to maintain rectification after the amalgam has melted.

The purpose of the gas within the tube is thus to aid in effecting the starting of its normal operation and after this has been efiected it becomes of relatively small importance, if indeed it is of any value in the further rectification. In fact it has been found that if rarefaction is carried on further after the normal functioning of the tube has been started this functioning appears to be improved by such rarefaction. Not only does the alkaline earth metal act as a source of electrons, but it also serves to lower the vapor pressure which might otherwise be that due to the mercury, as it is found in practice that the vapor pressure must be maintained at a relatively low point for best results. For example, if the amalgam or compound is permitted to boil, thus increasing the vapor pressure, the results are not nearly as satisfactory as when the temperature of the amalgam is kept closely to its melting point. In cases where the temperature of the amalgam has risen to a relatively high point so that the rectifier does not work properly, it has been found sufiicient to cool it as by placing it in cold water, whereupon rectification is again successfully carried on. Fig. 1'7 shows an apparatus capable of thus controlling the operative temperature of the rectifier container l; Under proper operating conditions there is a luminous glow are within the rectifier. Should a heavy arc discharge be permitted to take place within the rectifier, rectification stops at once. It is quite possible also that the compound vaporizes as such, instead of the mercury vapor serving by itself as the conducting element. If the vapor does occur as a barium mercury vapor rather than the mercury vapor alone, this would probably have a tendency to cause a higher efiiciency than with the mercury alone.

During operation the amalgam vaporizes and then condenses in the cooler parts of the walls of the container around the central tube H which defines with the outer wall a condensation chamber and drops down into its lower portion and mixes with the active alloy in the cathode pool. Possibly there is a change in the alloy such as an allotropic change in the formation of the crystals or a change in composition of the compound of the crystal and if this occurs it would be natural to expect it to give a more active electronic emission when such change is taking place. I believe that the constant melting, vaporizing, distilling and condensing with consequent compound-forming and dissolving that is going on while the device is rectifying tends to increase the natural electron emitting properties of the compound. Investigations which have been made by others as to the character of chemical combinations among metals appear to indicate that barium-mercury and strontium-mercury at least exist as compounds in equilibrium with the liquid phase of the amalgam at certain definite temperatures, but are decomposed at higher temperatures. For example, in the case of strontium and mercury, it has been shown that the compound SrHgm exists in mercury in equilibrium with the liquid the alkaline metals or earths which have been hereinbefore mentioned. In any event the rectification is found to be quite efficient and a small tube can successfully handle a very considerable output.

In Figure 6 a modified construction is shown in which the concentric tubes are arranged within the insulating block 50 instead of externally thereof as shown in Figure 1. It will be noted that this insulating block 50- is provided with a'plurality of annular portions of progressively increasing diameters toward its lower end, and engaging with the inner walls of these portions are the concentrically arranged or nested tubes 52,53, 54 and 55. The outer tube 55 dips within the amalgam 40 in the same manner as the tube 32 in Figure 1 and may have a vent opening 56 therethrough, and the lower ends of the other tubes 5|, 52, 53, and 54 are progressively further removed from the upper surface of the amalgam as the diameters of these tubes decreases. This progressive positioning of the lower end of the tubes, however, is on a more gradual slope than the upper ends of these tubes so that the smallest tube 5| is considerably longer than the next to the largest tube 54 and the tubes 52 and 53 are of intermediate lengths. Preferably these dimensions are so proportioned as to provide a uniform electrical capacity between adjacent pairs of tubes, the smaller the tubes the longer these tubes being so that the totalefiective dielectric areas are maintained the same. By this construction the stresses in the dielectric between the various pairs of adjacent tubes is substantially uniform throughout so that a higher potential difference may safely be carried between the anode and cathode without danger of breaking down the dielectric compris ing the gaseous atmosphere between the tubes. In any case, however, these tubes should preferably be placed closely together and the inner tube close to the anode so as to be spaced a distance from each other and the anode comparable to the normal mean free path of the electrons of the atmosphere within the rectifier, it being found that when electrodes having difference of potential impressed thereon and in a gaseous atmosphere are so placed, a very considerable difference of potential may be produced without causing ionization of the gas so that no current passes, though if such electrodes were separated a greater distance ionization would take place at the same potential difference and current would immediately pass. Thus, by placing the tubes close together, and particularly where these tubes are designed to present the same capacity gradient between them and the same potential gradient across the surface of the insulating block, a relatively high potential may be impressed on the terminals without passage of current from one to a succeeding tubular member. By this means the current passage is limited to that between the anode and cathode so that losses are greatly reduced.

This construction by which large potential differences are possible without danger of break down of the insulation or of the gaseous dielectric is of particular importance in a device of this description wherein only one half of the current wave is permitted to pass, the other being suppressed. This is for the reason that the direct current resulting is pulsating rather than uniform, and in order to make it suitable for many electrical devices, it is necessary to associate therewith choke coils and condensers in such a way as to produce a more nearly constant direct current flow. Where this is done the voltage impressed across the terminals of the device is at times nearly twice that of the normal alternating current voltage since during the suppression of one half of the alternating current wave when the voltage difference is one direction in the alternating current side, the voltage in the direct current side is in the opposite phase and only somewhat below the maximum. It will thus be seen that the actual diiference of potential across the rectifier terminals may be considerably more than the maximum alternating current potential. This alternating current line voltage must be sufficient in amount to start the rectifier, that is, high enough to start ionization of the gas between the anode and cathode above the surface of the amalgam and this with helium is in the neighborhood of 220 volts. With condensers and choke coils for smoothing the current, the voltage during the suppression of one side of the current wave might rise to nearly 400 volts.

Assuming this maximum voltage as 400 volts, and that there are three tubes between the outer cathode tube and the anode, the voltage drop from tube to tube will be 100 volts. This is insufficient to ionize helium gas or neon gas even should the tubes be spaced apart at a distance materially greater than the mean free path of the helium or neon electron. In practice about a sixteenth of an inch has been found suitable as a spacing between these tubes. These tubes also probably have some effect on the electric discharge in the gaseous atmosphere because of their distributed electrostatic field which most probably helps in the rectifying properties of the device. Equalization of the capacity gradient from tube to tube in construction of Figure 1 might be produced or approached by progressively decreasing the spacing of the inner and shorter tubes, though satisfactory results have been obtained with uniform spacing.

In Figures 8 and 9 is shown a construction of device designed to utilize both halves of the alternating current wave. In this construction there are two anodes, as at 60 each surrounded by a series 'of tubular members GI, 62, and 63, each of these tubular members being segmental in cross section and these nesting within an outer tube 64 of circular cross section which forms the cathode terminal and, dips into the cathode amalgam. The insulating block for carrying these tubes is provided with segmental shaped projections of progressively decreasing size, as at 66, 61 and 68, to which the upper ends of the tubular members GI, 62 and 63 may be fixed.

In Figure 13 is shown a similar construction except that in this embodiment the tubular members are nested within instead of externally of the insulating block, similar in this respect to Figure 6.

With either of these constructions the rectifier may be connected as shown in Figure 15, in which the alternating current is connected to the primary 10 of a transformer, opposite ends of the secondary H being'connected to the two anodes and the cathode being connected through the direct current load to the midpoint 12 of the secondary of thetransformer. Where the forms of the device shown in Figures 1 and 6 is employed, the direct current load may be arranged in series with the secondary 15 of the transformer and the rectifier as shown in. Figure 11,

the cathode being connected to one end of the secondary and the anode to the other end.

In Figure 10 is shown diagrammatically a construction suitable for use with three phase alternating current in which there are three anodes, as at 80, each having a series of tubes 8| or segmental cross section arranged thereabout and all of these tubes 8| being enclosed in a single tube 82 of circular cross section forming the cathode terminal and extending into the amalgam. With such a construction the alternating current lines 85, 86 and 81 may be connected to a three phase transformer having its primary windings 88, 89 and 90 connected in delta formation and its secondary windings 9!, 92 and 93 connected in star formation. Each of the anodes of the tube is connected to the alternating current lines 85, 86 and 81 and the single cathode is connected through the load to the central point of the star connection.

While certain embodiments of this invention have been illustrated, it should be understood that they are merely illustrative and that various changes and modifications might be made without departing from the spirit or scope of this invention as defined by the appended claims.

I claim:

1. An electric discharge device comprising a container containing a gaseous atmosphere at low pressure, an anode and a vaporizable and electron emitting cathode in said container, a tubular cathode lead surrounding said anode, an insulator between said anode and said cathode lead and concentrically arranged conductors extending from said insulator between said anode and said cathode lead, said conductors being spaced closely comparable to the mean free path of electrons in said atmosphere.

2. An electric discharge device comprising a container containing a gas at low pressure, an anode and a cathode in said container, a tubular cathode lead surrounding said anode, an insulator between said anode and said cathode lead and concentrically arranged conductors extending from said insulator between said anode and cathode, said conductors being spaced closely comparable to the mean free path of electrons in said gas, said cathode comprising an electropositive electron emitting substance.

3. An electric discharge device comprising a container containing a gas at low pressure, an anode and a cathode in said container, a tubular cathode lead surrounding said anode, an insulator between said anode and said cathode lead and concentrically arranged conductors extending from said insulator between said cathode and anode lead, said conductors being spaced closely comparable to the mean free path of electrons in said gas, said cathode comprising an electropositive electron emitting substance and a metallic vapor emitting substance.

4. An electric discharge device comprising a container, an annular cathode lead in said container, a cathode, aplurality of anodes arranged within said cathode lead, and means for producing a metallic vapor carrying electron emitting material between said cathode and anodes upon impressing differences of electrical potential between said cathode and any of said anodes.

5. -An electric discharge device comprising a container having a reentrant portion at its upper end'defining an annular chamber therearound, an anode extending into said container at said reentrant portion, a cathode lead surrounding said anode and extending toward the lower end of said container, and a cathode comprising a vaporizable electron emitting material in said container in contact with the lower portion of said cathode lead.

6. An electric discharge device comprising a container having a reentrant portion at its upper end defining an annular chamber therearound, an anode extending into said container at said reentrant portion, a cathode lead surrounding said anode and extending toward the lower end of said container, a cathode in contact with said lead, and conducting plates surrounding the lower end of said anode and' spaced therefrom and from each other to form plates of a series of electrical condensers between said anode and said cathode lead.

'7. An electric discharge device comprising a container having a reentrant portion at its upper end defining an annular chamber therearound, an anode extending into said container at said reentrant portion, a cathode lead surrounding said anode and extending toward the lower end of said container, a cathode in contact with said lead, and conducting plates surrounding the lower end of said anode and spaced therefrom and from each other to form plates of a series of electrical condensers of substantially equal capacity between said anode and said cathode lead.

8. An electric discharge device comprising a container having a reentrant portion at its upper end defining an annular chamber therearound, an anode extending into said container at said reentrant portion, a cathode lead surrounding said anode and extending toward the lower end of said container, a cathode in contact with said lead and conducting plates surrounding the lower end of said anode and spaced therefrom and from each other to form plates of a series of electrical condensers of substantially equal capacity between said anode and said cathode lead, said plates being closely spaced a distance comparable to the mean free path of the electrons in said container.

9. An electric discharge device comprising a container, a plurality of anodes in said container, a single vaporizable and electron emitting cathode in said chamber, a tubular cathode lead surrounding said anodes and a series of spaced conductive plates between each of said anodes and said cathode lead acting to produce a gradual voltage gradient between said anodes and said cathode.

10. An electric discharge device comprising a container having a rarefied gas therein, a plurality of anodes and a single cathode in said container, said cathode comprising an electron emitting material and an easily vaporized conducting material, a cathode lead surrounding said anodes, and a series of conductors between each of said anodes and said cathode lead spaced apart a distance comparable to the mean free path of an electron of said gas and vapor.

11. An electric discharge device comprising a container having a rarefied gas therein, a block of insulation supported in said container and having concentric surfaces of progressively inhaving concentric surfaces of progressively increasing circumferences, an anode extending into said container concentrically of said surfaces, a tubular conductive element lapping past each of said surfaces, said elements extending away therefrom in parallel spaced relation, a tubular cathode lead surrounding said conducting elements, and a cathode comprising a'pool of mercury and an electro-positive electron emitting material into which said cathode lead extends, said cathode being out of contact with said elements and anode.

13. An electric discharge device comprising a low pressure gas container having a reentrant portion defining therearound an annular condensation chamber, a plurality of anodes extending through said reentrant portion, a tubular cathode lead surrounding said anodes, a cathode comprising a pool of mercury and an electron emitting material into which said cathode lead extends, and a series of spaced conducting plates extending between each anode and said cathode lead out of contact with said pool, said plates being spaced apart a distance comparable to the mean free path of a gas electron in said container, and each adjacent pair of each series of plates forming opposite plates of an electrical condenser, the capacities of all of said condensers being substantially equal.

14. An electric discharge device comprising a v container, vaporous conductive material at low pressure within said container, an anode and a vaporizable and electron emitting cathode material in said container, and means for subjecting said conductive material between said electrodes to a distributed electrostatic field.

15. An electric discharge device comprising a container having a rarefied gas therein, a block of insulation supported in said container and having concentric surfaces of progressively increasing circumferences, an anode extending into said container concentrically of said surfaces, a tubular conductive element lapping past each of said surfaces, said elements extending away therefrom in parallel spaced relation, a tubular 

